Walking catfish a troublesome exotic in The Everglades (National Park)

Exotic fish pose threat to native species in Everglades

BY CURTIS MORGAN

The small pond six miles deep in Everglades National Park suddenly began bubbling like a pot aboil -- a telltale sign of air-slurping walking catfish.

Dave Hallac, the park's chief biologist, dipped a net into the muddy commotion and hauled up a mess of wriggling slime so hefty it surprised even him. He counted out 56 fish from a single scoop.

Walking catfish, along with other species originally imported for somebody's tank or table, outnumbered natives in this shallow, shady bayhead by an unhealthy margin. Unlike giant python, the Glades' most notorious invader, these dinky denizens don't draw attention to their presence by, say, swallowing an alligator and exploding. But for park scientists, their spread is no small concern.

''This is a problem that is 10 times worse than the python, but it's all under water, so nobody knows about it,'' Hallac said.

Florida's canals and lakes have sheltered tropical imports for decades, with 34 species known to be reproducing. There have long been plenty in the park as well. A weathered sign at the popular Anhinga Trail, built along a pit dredged for road fill, explains that many fish seen from the boardwalk aren't locals.

Since 2000, however, park scientists have charted a surge of invasives. Fishery biologist Jeff Kline documented one species, the African jewelfish, going from nowhere to just about everywhere in less than a decade. That's stunningly swift. At least 16 exotics have been caught in the park freshwater zone, and some have pushed deep into isolated marshes where tourists never trek.

''In some ways,'' Kline said, ``it's a form of pollution.''

Ironically, the prime suspect for the exotic increase is a federal project to revive the park's parched eastern side: basins built to store rain water and runoff from adjacent canals. It's an unintended consequence, Hallac said, that engineers designing future projects to restore the natural flow to the River of Grass will need to consider.

The theory, said Kline, is that exotics move from the basins and canals as summer rains flood the marsh. When waters recede, some manage to survive the same way that natives do -- in caverns called ''solution holes'' in the limestone bedrock and bayhead pools in the deeper marsh.

STRANGE BEDFELLOWS

There is little dispute that fish from Thailand, Costa Rica and West Africa shouldn't be sharing marshy shallows with shellcrackers and mosquitofish. The big worry is that the boom will disrupt the food chain, with invaders competing with or even eating natives that fatten herons, egrets and other wading birds.

The drainage canals crisscrossing South Florida, deep and warm, offer a perfect refuge for many tropical imports, said Paul Shafland, longtime director of the Florida Fish and Wildlife Conservation Commission nonnative fish lab.

And once they're in an open waterway, they're almost impossible to get out.

''We cannot do that without eliminating 100 percent of everything else,'' he said.

The FWC outlaws the intentional release of exotics, but, Shafland pointed out, it remains undetermined what, if any, ecological threat they pose.

The walking catfish, an air-breather named for its ability to shimmy short distances on stiffened fins, earned dire headlines in the 1960s as a monster threatening to take over the Glades long before pythons ever slithered into the media spotlight.

The catfish did indeed march across the Glades and much of the state -- at least in the tolerably warm waters of the southern half -- but researchers have yet to pinpoint impacts on natives.

Shafland likened exotic fish to foreign bacteria -- ''99.9 percent innocuous'' -- with a minute percentage potentially harmful.

''They could create a serious problem somehow, somewhere,'' Shafland said, but he added, ``I believe the aquatic ecosystem is far more resilient and resistant to disturbance than probably people in the park do.''

Park scientists acknowledge the uncertainty. Herons certainly can't tell between a three-inch pike killifish, which hails from Central America, and an Everglades killfish. Without a biologist along, neither could most humans. (The invader's tiny snout is longer and has more hairlike teeth.)

And there may be little they can do about the invaders already deep in the Glades. Near-freezes, like the one last week, help by killing many of the cold-sensitive tropicals, but populations have historically rebounded, Hallac said.

''It really only sets them back for that season,'' he said.

SLOWING SPREAD

If the fish can't be stopped, Hallac said the park needs to begin developing methods to slow down the spread. In an Everglades system under threat from all manner of invasive species -- from climbing ferns to constricting snakes -- there is also risk that the next exotic could be the tipping point.

The park, Hallac said, was created with the mission of preserving the Everglades in its natural state, right down to the fish nobody notices in stagnant ponds.

The pond so thick with walking catfish also was dense with jewelfish, which filled fish traps set the day before by the dozens.

''This belongs in a fish tank,'' said Hallac, tossing one of the muddy green fish into a bucket. `It shouldn't be in a national park.''